Picture reproducing apparatus



Feb. 18, 1941.

W. A. TOLSON PICTURE REPRQDUCING APPARATUS 1 Filed Sept. a0, 1936 2 Sheets-Sheet 2 HORIZONTAL 'SY/VCHHO/V/Z/NG /VER7'/C/7L nSY/VCHIPO/V/Zl/VG IMPULSE ISnventor Vl/illiam H. Tel-son,

B; 7% dtwmeg Patented Feb. 18, 1941 UNITED STATES PICTURE REPRODUCING APPARATUS William A. Tolson, Merchantville, N. J., assi nmto Radio Corporation of America, a corporationof Delaware Application September so, 1936, Serial No. 103371 Claims.

My invention relates to picture reproducing apparatus and particularly to the separation of picture signals and synchronizing signals.

In a preferred type of television system, syn- 5 chronization between scanning at the transmitter and scanning at the receiver is obtained by transmitting a horizontal synchronizing impulse at the end of each scanning line and a vertical synchronizing impulse at the end of each picture frame, the latter impulse being of greater duration than a horizontal synchronizing impulse. All synchronizing impulses are of greater amplitude than the picture signals. Such a system is described in British Patent 407,409. An improved system for transmitting a composite signal of this character is described in Patent No. 2,192,121, issued Feb. 2'7, 1940, in the name of A. V. Bedford, and assigned to Radio Corporation of America.

At the receiver, suitable means are provided for separating the picture and synchronizing impulses, whereby only the synchronizing impulses are supplied to the cathode ray deflecting circuits, and for separating the horizontal and vertical synchronizing impulses.

In a system of the above described type, difiiculty has been experienced due to variations in the amplitude of the synchronizing impulses. impressed upon the deflecting circuits. Such variations may becaused by noise signals superimposed upon the synchronizing impulses, by 60- cycle hum introduced at any point in the picture channel, or by phase shift.

Such variations in amplitude make the adjustment of the deflecting circuit oscillators more critical than desired when the deflecting circuits are of the preferred type employing relaxation oscillators, blocking oscillators, or the like. If the oscillators are not adjusted properly, the edges of the picture pattern become irregular and the picture has a tendency to tear out at the point where the synchronizing impulses are of minimum amplitude.

It is accordingly an object of my invention to provide an improved method of and means for separating picture and synchronizing signals.

It is a further object of my invention to provide an improved method of and means for I supplying synchronizing impulses of substantially constant amplitude to cathode ray deflecting circuits.

It is a further object of my invention to provide an improved method of and means for sepr, arating horizontal and vertical synchronizing impulses.

(Cl. 178-75) I In practicing a preferred embodiment of my invention, a cathode ray tube is employed which is provided with a plurality of target plates. These plates are sopositioned at one end of the cathode ray tube that when the cathode rayis deflected by a composite signal consisting of picture signals and synchronizing impulses, the picture signalscause the cathode ray to be deflected along'a line on one target plate while the synchronizing irnpu1ses cause it to be deflected 10 further alongthe same, line. on another target plate. 'Sincethe" beam current, that is, the intensity of the cathode 'ray,'is constant, the signal supplied to the second-mentioned target plate is constant, there being no variation in the signal derived from. this-plate regardless of the amplitude of the, synchronizing impulses.

In another embodiment'of the invention, an additional target plateis provided for the purpose of producing abiasing voltage which is applied to the cathode ray deflecting plates whereby the picture impulses are prevented from deflecting the cathode ray against the synchronizing output target plate when the incoming signals increase in amplitude If desired, the amplitude of the horizontal synchronizing impulses may be reduced with respect to the vertical synchronizing impulses before the composite signal is applied to the cathode ray deflecting plates whereby the vertical synchronizing impulses will deflect the cathode ray through a greater angle than will the horizontal synchronizing impulses. By providing an additional target plate so positioned that it is struck by the, cathode ray each time it is deflected by the vertical synchronizing impulses but not by the horizontal synchronizing impulses, the; vertical synchronizing impulses may be taken off this target plate to the exclusion of the other synchronizing impulses.

, The invention will be better understood from the following description, taken in connection with theaccompanying drawings, in which Figure 1 is a circuit diagram of one embodiment of my invention,

Figure 2 is a diagram which is referred to in explaining the operation of the circuit shown in Figure 1, I v

Figure 3 is a circuit diagram of another embodiment of my invention, and

Figures 4, 5, 6 and 6a. are diagrams which are referred to in explaining the operation of the circuit shown in Figure 3.

Referring to Fig. 1 I have shown my invention applied to a television receiver which is designed to receive picture and synchronizing impulses which have been transmitted by means of a modulated carrier wave in accordance with the teachings of the above mentioned British patent or Bedford application. The receiving apparatus includes a radio receiver I which selects and demodulates the desired carrier wave whereby picture signals and synchronizing impulses of the character described above appear in the output circuit thereof. I

Picture signals and synchronizing impulses are amplified in a signal channel including resistance coupled amplifiers 2 and 3, and are impressed upon the control grid 4 of the usual cathode ray receiver tube 6. The cathode ray receiver tube 6 may be of well known construction comprising an evacuated envelope having therein a cathode 1, the control grid 4, a first anode 8 and a second anode 9. Suitable deflecting means such as deflecting coils II and I2 are provided for deflecting the cathode ray both horizontally and vertically to effect scanning of a fluorescent screen l3 at the end of. the tube.

The horizontal deflecting coils II are supplied with saw-tooth current having a comparatively high frequency from a horizontal deflecting circuit M. The vertical deflecting coils |2 are supplied with saw-tooth current having a comparatively low frequency from a vertical deflecting circuit Hi. The deflecting circuits M and I6 may be any of several designs, such asa circuit including, for example, a blocking oscillator which can be locked in step with synchronizing impulses impressed thereon.

The number of amplifier stages in the radio receiver is so selected that the polarity of the synchronizing impulses impressed upon the control grid 4 of the cathode ray tube 6 is negative whereby the cathode ray is blocked at the end of each scanning line, this being desirable in order to prevent a trace on the fluorescent screen I 3 during the return line period.

The scanning of the fluorescent screen I 3 by the cathode ray is maintained in synchronism with the scanning at the transmitter by separating the synchronizing impulses from the picture signal and impressing these impulses upon the deflecting circuits l4 and Hi. In accordance with my invention, the separation of the picture and synchronizing signals. is accomplished by supplying the composite signal through a coupling condenser IT to the deflecting plates 8, or other suitable deflecting devices, of a cathode ray tube |9.

The cathode ray tube I9 may be conventional in construction except for target plates 2| and 22 provided at the end of the tube. The particular tube illustrated includes the usual indirectly heated cathode 23, a control grid 24, and an anode 26. Preferably the control electrode 24 is biased slightly negative, while suitable positive potentials are applied to the anode 26 and to the target plates 2| and 22 by means of batteries 21 and 28 or other suitable voltage sources.

Preferably the deflecting plates l8 are maintained at approximately the same direct current potential as the target plates 2| and 22, the lower deflecting plate being connected through a conductor 29 to the positive terminal of the battery 28 and the upper deflecting plate being connected to the same positive terminal through a resistor 3| of high resistance value.

The target plate 2|,which is in the path of the cathode ray while it is being deflected by the picture signal, is connected directly to the positive terminal of the battery 28 while the target plate 22, which is in the path of the cathode ray only while it is being deflected by the synchronizing impulses, is connected to the same positive terminal through an output resistor 32. As will be explained more fully hereinafter, synchronizing signals of substantially constant amplitude appear across the resistor 32. These signals are amplified by a suitable amplifier 33 and supplied to a separating circuit 34, such as a filter circuit consisting of resistors and condensers (not shown), for separating the horizontal synchronizing impulses from the vertical synchronizing impulses. The horizontal and vertical synchronizing impulses are then supplied to their respective deflecting circuits l4 and I6.

Considering the operation of the cathode ray tube |9 more in detail, the composite signal which is supplied to the deflecting plates is indicated by the curve 36 in Fig. 2. This curve shows the signal as it would appear on a cathode ray oscillograph. It will be understood that the composite signal causes the cathode ray of the tube I9 to move only in the plane of the paper whereby the trace of thecathode ray on the target plates 2| and 22 is a line as indicated on the plates shown at the right hand side of Fig. 2.

The composite signal shown in Fig. 2 is of the character transmitted by the system described in the above mentioned Bedford application. The signal consists of picture signals indicated at m, blanking signals or pedestals indicated at n, and synchronizing impulses 0 which are superimposed on the pedestals n. In the curve 36, only horizontal synchronizing impulses are shown.

In the particular case assumed in. Fig. 2, the alternating current axis of the composite signal is so located that no direct current bias on the deflecting plates I8 is required for satisfactory operation. If there is no bias on the deflecting A plates l8, the cathode ray will be undeflected and will strike the target plate 2| at the point is when there is no incoming signal. Since the top of the pedestals n represents black, it is apparent that picture signals will not deflect the cathode ray off the target plate 2|. i

The synchronizing signals, however, will deflect the cathode ray through a greater angle and will cause the cathode ray to move along a line on the upper target plate 22 as indicated in Fig. 2. Thus, each time a synchronizing impulse is impressed upon the deflecting plates l8 the cathode ray is deflected against the target plate 22 and a synchronizing impulse appears across the output resistor 32. Since the synchronizing impulses o are all of the same width, as shown in the curve 36, the cathode ray will be on the target plate 22 for the same length of time for each synchronizing impulse, and since the beam circuit is con stant the signal appearing across the output resistor 32 will be independent of the position of the cathode ray on the plate 22. As a result, within the operating limits of the equipment, the synchronizing impulses supplied to the amplifier tube 33 will be of substantially constant amplitude, regardless of the amplitude of incoming signals.

, Since in most cases of picture transmission the height of the pedestals n with respect to the alternating current axis is not constant, this height being varied for the purpose of obtaining background control, it is desirable to apply a direct current bias to the deflecting plates |8 which varies automatically in accordance with the character of the incoming signal. Apparatus for ob.-

taining this result is shown in Fig. 3. In Figs. 1 and 3 like parts are indicated by the same reference numerals.

Referring to Fig. 3, a cathode ray tube 31, similar to the tube I9 in Fig. 1, is employed for separating picture and synchronizing signals; the two cathode ray tubes l9 and 31 may .be identical except for the number and arrangement of target plates at the end of the tube. In the improved circuit the cathode ray separating tube 31 has four target plates a, b, c and d, the tar-' get plates a and b performing the same functions as the target plates 2| and 22, respectively, in Fig. 1, and the target plates and. dacting to provide bias to the deflecting plates l8 and to separate out the vertical synchronizing impulses, respectively.

It will be evident from the description which follows that the target plate d may be omitted if desired, and the separating tube 31 employed in combination with a separating circuit such as indicated at 34 in Fig. 1. In that case the composite signal may be supplied directly to the deflecting plates [8 from the amplifier tube 2 as in Fig. 1. When the plate (2 is employed, however, the composite signal should be supplied to the deflecting plates l8 through a suitable amplifier 38 or through a filter (not shown) for reducing the amplitude of the comparatively high frequency horizontal synchronizing impulses with respect to the amplitude of the vertical synchronizing impulses. The signal is taken from amplifier 3 in order to keep the synchronizing impulses of positive polarity at the plates I8.

In the specific circuit illustrated, this reduction in amplitude of horizontal synchronizing impulses is obtained by omitting the peaking coil in the plate circuit of the amplifier 38 and by increasing the resistance of its plate resistor 39. Obviously, the high frequency response of the amplifier 38 may be reduced in other ways, there-by reducing the amplitude of the horizontal synchronizing impulses. The connections of the target plates a and b are the same as those of the corresponding target plates 2| and 22 shown in Fig. 1, the output resistor for horizontal synchronizing impulses being indicated at R3. The target plate 0 is connected to the positive terminal of the battery 28 through a resistor R2 which is shunted by a condenser 4!. As will be understood from the following description, the time constant of the circuit consisting of the condenser 4| and resistor R2 is made such that a bias is applied to the deflecting plates [8 which changes slowly with respect to the time required for scanning a single line.

The target plate d is connected through an output resistor R1 to the positive terminal of the battery 28. The vertical synchronizing signals appear across resistor R1 and are supplied to the vertical deflecting circuit l6, while the horizontal synchronizing impulses appearing across the resistor R3 are supplied to the horizontal deflecting circuit M. Since the synchronizing impulses are of negative polarity when taken ofi the resistors R1 and R3, there should be an amplifier stage for reversing their polarity before they are impressed upon the grid of a blocking oscillator. Such an amplifier is included in each of the deflecting circuits indicated at I 4 and IS.

The way in which separation of horizontal and vertical synchronizing impulses is obtained will be understood by referring to Fig. 4, where the composite signal supplied to the deflecting plates I 8'is shown by the curve 42. Fig. 4 indicates the deflection of the cathode ray by this signal with respect to the target plates a, b, c, d. It will be noted that the horizontal synchronizing impulses indicated at 0 cause the cathode ray to be deflected across the plate b and against the plate 0. However, these signals do not have sufilcient amplitude to deflect the cathode ray against the plate (1. A vertical synchronizing impulse does have sufiicient amplitude to deflect the cathode ray against the plate 02 whereby only vertical synchronizing impulses appear across the output resistor R1. a

It may be noted that the cathode ray will traverse plate 7) due to the leading and trailing edges of the vertical impulse, and. will produce high-frequency impulses across R3. These impulses will do noharm, however, since they do not occur at the correct time to trigger the oscillator of the horizontal deflecting circuit. These unwanted impulses will be of much shorter duration than the horizontal impulses, and may be reduced in amplitude relative to the horizontal synchronizing impulses by means of frequencydiscriminating circuits, if desired. The action of the separating circuit as a result of the horizontal synchronizing impulses striking the target plate 0 will be understood by referring to Figs. 5 and 6.

In Fig. 5 the curve 43 represents an incoming signal which is supplied to the deflecting plates !8. It will be noted that at'the left hand side of the curve 43 the picture signal is of much greater amplitude than the picture signal atthe right hand side of the curve 43. Since the height of a pedestal n with respect tothe A. C. axis increases with increase in amplitude of picture signal, the picture signals and the pedestals will cause the cathode ray to-be deflected against the target plate b if they are of 'sufliclent amplitude. This is indicatedjin Fig. 5, where the tops of certain' pedestals and some of the picture signals representing black appear above the dotted line 44 indicatingthe bottom edge of the target plate b. a a

The operation of my improved circuit shown in Fig. 3 is indicated by the diagram in Fig. 6. In Fig. 6 it is assumed that the same picture signal as that indicated in Fig. 5 is supplied to the deflecting plates l8. As a result of the horizontal synchronizing impulses deflecting the cathode ray against the plate 0, a flow of current is produced through the resistor R2 whereby the target end of resistor R2 becomes negative. This negative potential is applied to the upper plate l8 through resistor 3|, thus causing the cathode ray to be deflected downwardly. This action is indicated in Fig. 6 where the composite signal of the greater amplitude is shown moved down with respect to the target plates as a result of the biasing voltage. This automatic biasing action keeps the cathode ray deflected downwardly just enough so that the cathode ray is deflected upon or close to the edge of. the target plate 0 during the usual variations in the amplitude of the composite signal;

Before explaining the operation of the biasing circuit in more detail, it should bepointed out that the variationin amplitude of the pedestals n with respect to the AC. axis (as they appear in the output circuits of amplifiers: 2 and 3) cannot take place as rapidly as indicated in Figs. 5 and 6, there not being enough space on the drawings to show the variation accurately. This is because an alternating current amplifier-always has a certain low frequency time constant. The change in amplitude will occur gradually, over a period including forty horizontal synchronizing impulses, for example, and likewise the depressing of the A. 0. axis by the bias voltage (as shown in Fig. 6) will require a time period of the same order.

The specific manner in which the horizontal synchronizing impulses act to provide biasing for the deflecting plates depends to a certain extent upon their wave shape. If the tops of these impulses are rectangular, the action will be substantially as follows: Incoming signals of an intermediate amplitude will cause the cathode ray to be deflected against the plate 0 each time a synchronzing impulse occurs, until a charge has been built up across the condenser 4| sufflcient to deflect the cathode ray downwardly enough to prevent succeeding synchronizing impulses from deflecting it against the plate 0. After a small amount of the charge leaks oii the condenser 4|, the cathode ray is again deflected against the plate 0 by a succession of synchronizing impulses. These synchronizing impulses continue to deflect the cathode ray against the plate 0 until a charge has been built up in the condenser 4| of sufficient value to again deflect the cathode ray to a position where the synchronizing impulses cannot deflect it against the plate c.

As a matter of fact, in the usual television receiver the tops of the synchronizing impulses are rounded, because of the inability of the television system to transmit the high frequency compo- 1 nents representing the sharp corners of rectangular impulses. Therefore, the top of a horizontal synchronizing impulse will have a shape similar to that shown in Fig. 6a. When the tops of the impulses have such a shape, the top of the impulse being narrower than the lower part of the impulse, it is not necessary that the biasing action be exactly as described above. Instead, the cathode ray may be deflected against the plate 0 by all the horizontal synchronizing impulses, the height of the deflection on the plate 0 depending upon the degree of biasing required.

Thus, referring to Fig. 60, if the incoming signals are of intermediate amplitude, the cathode ray is deflected slightly above the bottom edge of the plate c, the said bottom edge of the plate 0 being indicated by the dotted line 4'! for this particular deflection. It will be noted that the cathode ray is on the plate 0 for the time ii. If the amplitude of the incoming signals increases, the cathode ray is deflected further up on the plate c, as indicated in Fig. 6a, where the dotted line 48 represents the bottom edge of the plate 0 for this deflection. During this second deflection, the cathode ray is on the plat-e c for the time t2. Obviously, the longer the cathode ray rests on the plate 0, the greater will be the charge supplied to the condenser 4|. Therefore, the biasing supplied to the deflecting plates I8 is increased or decreased in accordance with the amount the cathode ray is deflected upwardly on the plate 0.

From the foregoing description, it will be apparent that various modifications may be made in my invention without departing from the spirit and scope thereof, and I desire, therefore, that only such limitations shall be placed thereon as are necessitated by the prior art and set forth in the appended claims.

I claim as my invention:

1. In a television receiver of the type in which picture signals and synchronizing signals are applied to a cathode ray tube and in which deflecting circuits are utilized to deflect the cathode ray in said tube whereby a picture is reproduced therein, the method of separating said synchro nizing signals from said picture signals where all of said signals are transmitted as a composite signal with the synchronizing signals of greater amplitude than the picture signals, said method comprising deflecting a second cathode ray in accordance with all of said signals, and utilizing said second cathode ray to produce a synchronizing impulse each time the deflection of said second ray exceeds a certain predetermined amplitude whereby said synchronizing impulses may be, applied to said deflecting circuits substantially to the exclusion of said picture signals.

2. In a television receiver of the type in which picture signals and horizontal and vertical synchronizing impulses are applied to a cathode ray tube and in which deflecting circuits are utilized to deflect the cathode ray in said tube whereby a picture is reproduced therein, the method of separating said horizontal synchronizing impulses from said vertical synchronizing impulses where they are transmitted as a composite signal with the vertical impulses occurring at a lower frequency than the horizontal impulses, said method comprising deflecting a second cathode ray within certain limits in accordance with said horizontal impulses, deflecting said second cathode ray beyond said certain limits in accordance with said vertical impulses, and utilizing said second cathode ray to produce in a desired circuit only said vertical synchronizing impulses in response to the deflection of said second ray being deflected beyond said limits whereby said vertical synchronizing impulses only may be applied to one of said deflecting circuits.

3. In a television receiver of the type in which picture signals and horizontal and vertical synchronizing impulses are applied to a cathode ray tube and in which deflecting circuits are utilized to deflect the cathode ray in said tube whereby a picture is reproduced therein, the method of separating said horizontal synchronizing impulses from said vertical synchronizing impulses where they are transmitted as a composite signal with said horizontal and vertical impulses having approximately the same amplitude and with said vertical impulses occurring at a lower frequency than said horizontal impulses, said method comprising reducing the amplitude of one group of synchronizing impulses with respect to the other group of synchronizing impulses, deflecting asecond cathode ray in accordance with said impulses, and utilizing said second cathode ray to produce in a desired circuit only one group of said synchronizing impulses in response to the deflection of saidsecond ray exceeding a certain predetermined amplitude whereby said one group of synchronizing impulses may be applied to one of said deflecting circuits substantially to the exclusion of the other group of synchronizing impulses 4. In a television receiver of the type in which picture signals and horizontal and vertical synchronizing impulses are applied to a cathode ray tube and in which deflecting circuits are utilized to deflect the cathode ray in said tube whereby a' picture is reproduced therein, the method of separating said horizontal synchronizing impulses from said vertical synchronizing impulses where they are transmitted as a composite signal with said horizontal and vertical impulses having approximately the same amplitude and with said vertical impulses occurring at a lower frequency than said horizontal impulses, said method comprising reducing the amplitude of said horizontal impulses with respect to said vertical impulses, deflecting a second cathode ray in accordance with said impulses, and utilizing said second cathode ray to produce in a desired circuit only said vertical synchronizing impulses in response to the deflection of the second ray exceeding a certain predetermined amplitude whereby said vertical synchronizing impulses only may be applied to one of said deflecting circuits.

5. A television receiver comprising a cathode ray tube and deflecting circuits associated therewith for deflecting the cathode ray, an amplifier for supplying picture signals and synchronizing signals to said cathode ray tube, a synchronizing channel to which picture signals and synchronizing signals are supplied from said amplifier, means in said channel for separating said picture signals and said synchronizing signals where the synchronizing signals are of greater amplitude than the picture signals, said separating means including a second cathode ray tube including a target plate and means for producing a cathode ray, deflecting means for said second tube, means for supplying all of said signals to said deflecting means whereby said ray is deflected in accordance with all of said signals, said target being so located that said synchronizing signals only deflect said ray against it, and means for taking synchronizing signals 01f said plate and supplying them to said deflecting circuits.

6. A television receiver comprising a cathode ray tube and deflecting circuits associated therewith for deflecting the cathode ray, an amplifier for supplying picture signals and synchronizing signals to said cathode ray tube, a synchronizing channel to which picture signals and synchronizirg signals are supplied from said amplifier, means in said channel for separating said picture signals and said synchronizing signals where the synchronizing signals have a greater amplitude than the picture signals, said separating means comprising a second cathode ray tube including means for producing a cathode ray and a plurality of target plates so positioned that said second ray may be deflected against them, defleeting means for said second cathode ray tube, means for supplying said signals to said deflecting means, one of said target plates being so positioned that said second ray strikes it during deflection by said picture signals and another of said plates being so positioned that said sec ond ray strikes it only during deflection by said synchronizing signals, and means for taking synchronizing signals off said last mentioned plate and supplying them to said deflecting circuits.

7. A television receiver for the reception of a composite signal comprising picture signals and synchronizing signals, the synchronizing signals having a greater amplitude than the picture signals, said receiver comprising a cathode ray tube and deflecting circuits associated therewith for deflecting the cathode ray, an amplifier for supplying said picture signals and said synchronizing signals to said cathode ray tube, a synchronizing channel to which said picture signals and said synchronizing signals are supplied from said amplifier,meansin said channel comprising a second cathode ray tube having deflecting means, means for impressing said composite signal upon said deflecting means, and means for producing synchronizing signals in response to the second cathode ray being deflected more than a predetermined amount whereby they may be supplied to said deflecting circuit substantially to the exclusion of said picture signals.

8. In a television receiver for the reception of a composite signal comprising picture signals and synchronizing signals, the synchronizing signals having greater amplitude than the picture signals, a cathode ray tube including means for generating an electron beam, deflecting means for said tube, a target plate so positioned that it will be struck by said beam when it is deflected a certain amount, a second target plate so positioned that it will be struck 'by said beam when it is deflected an. amount greater than said certain amount, means for supplying said composite signal to said deflecting means with its polarity and amplitude such that said synchronizing signals onlydeflectsaid beam against said first target plate, means for taking synchronizing signals off said first target plate, means including a resistor shunted by capacity for taking signals off said second target plate, and means for biasing said deflecting means in accordance with the voltage drop across said resistor.

9. Apparatus for separating picture signals and synchronizing signals where the synchronizing signals are of greater amplitude than the picture signals, said apparatus including a cathode ray tube including a target plate and means for producing a cathode ray, deflecting means for said tube, means for supplying all of said signals to said deflecting means whereby said ray is deflected in accordance with all of said signals, said target being so located that said synchronizing signals only deflect said ray against it, means for taking synchronizing signals off said plate, and means for so applying a bias deflection to said cathode ray in accordance with the amplitude of the incoming signals that there is an increase in said bias deflection which increases the distance between the edge of said plate and the alternating current axis of the deflected cathode ray in response to an increase in picture signal amplitude.

10. In a television receiver for the reception of -a composite signal comprising picture signals and synchronizing signals, the synchronizing signals having a greater amplitude than the picture signals, a cathode ray tube having deflecting means, means for impressing said composite 

